Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 20,725	$ 18,611
Other comprehensive income, net of tax
Net change in fair value of securities available for sale	531	4,081
Net change in fair value of cash flow hedges	89	123
Net change in other comprehensive income for defined benefit postretirement plans	78	60
Total other comprehensive income	698	4,264
Total comprehensive income	$ 21,423	$ 22,875